1. Technical Field
The present invention relates to a heat radiation reflective film and a method for producing the film, and a heat radiation reflector which includes the heat radiation reflective film.
2. Description of Related Arts
In recent years, a growing interest in energy conservation measures results in a growing demand for a heat radiation reflective film which blocks the transmission of solar heat through the window glass of a building and a vehicle to reduce the load on a cooling system.
The spectrum of the solar light ranges from the ultraviolet to the infrared. Visible light, which corresponds to a color range of violet through yellow to red and a wavelength range of from 380 nm to 780 nm, occupies about 45% of the solar light. Infrared light occupies about 50% of the solar light. Infrared light includes the near-infrared light (wavelength range of from 780 nm to 2500 nm) near the visible region and the mid-infrared light in above the range. The light energy in the infrared region is as low as about one tenth or less of the light energy in the ultraviolet region, while infrared light has great thermal effects. When infrared light is absorbed by a material, the absorbed energy is converted into heat, which is then radiated into the atmosphere, thereby increasing the temperature. Therefore, infrared light is also called heat radiation. Blocking of such radiation allows preventing a temperature rise in the room. The blocking also allows preventing heat within the room from dissipating into the environment during the winter in cold climates.
Heat radiation reflective films produced by laminating high refractive index layers and low refractive index layers alternately by a deposition method or a dry film forming method such as a sputtering method have been previously proposed (see, for example, Patent Document 1). The dry film forming method, however, results in increase in manufacturing costs. And with this method, it is difficult to produce a heat radiation reflective film with a large surface area, and problems such as limitation to heat-resistant materials arise.
To address these problems, methods of using rutile-type titanium oxide particles which are surface-treated with a heterocyclic nitrogen compound, and a UV-cured resin to form a high refractive index layer are disclosed (see, for example, Patent Documents 2 and 3).
As the methods, however, include laminating a low refractive index layer and a high refractive index layer alternately by repetition of application, drying, and curing, the interfaces between the layers are distinct, and the bond strength between the layers is low. Thus, application of a high peel force results in delamination of layers.